1. Field of the Invention
This invention relates to a circuit arrangement for a telecommunication system, and more particularly to a circuit arrangement for a telephone auxiliary exchange having a delayed connection of a busy signal after the release of the busy connection set on the basis of a release of one of the two connecting stations involved in a connection. The present invention is contemplated for use in a system such as that disclosed in U.S. Pat. No. 4,009,351.
2. Description of the Prior Art
German Auslegeschrift No. 1,242,275, incorporated herein by this reference, discloses a circuit arrangement in which the busy signal is transmitted to the calling subscriber from a busy signal set when a connection does not take place, or on the occurrence of a back release of a connection generated or to be generated by means of a central setting device, the busy signal requesting the subscriber to hang up his receiver and to therewith release the total connection. In this known arrangement, the connection of the busy signal set results after the release of the busy connection set, and is done for the purpose of providing the busy signal to a calling subscriber and for monitoring to determine hang up by the calling subscriber. Before the release of the connection set is induced, the subscriber station, not yet released, is first identified in order to control the connection of this subscriber location with a free busy signal set with the aid of the central setting device and with the utilization of selective switching equipment of a search device and for the subsequent release of the connection set.
In this known arrangement, time switching equipment is assigned to the connection set to be released, the time switching equipment capable of delaying the start of the central search equipment, so that the connection of the special busy signal set can be saved when the respective subscriber immediately hangs up his receiver after determining the end of the connection.
The central control equipment in this known arrangement is to be utilized for the recoupling of busy signal sets. A reduction of the holding time of the connection sets is only partially obtained by the time delay introduced for the connection of the busy signal set. The additional load time in the coupling field due to the longer holding of the coupling points for switch-through to the connecting set can also not be reduced.
It has been proven, for example in respect to the German Postal Service, that the number of house interconnection sets to be provided is greater than the traffic requires due to operating regulations. In contrast thereto, the number of exchange transmissions and tie line transmissions is precisely adjusted, for the most part, to the traffic increase. It has also been proven that with the release of a subscriber station which is part of a connection, the other subscriber station also definitely releases the connection, although such release is delayed. The time span between the release of the one, for example, the calling subscriber station, and the release of the other, for example the called subscriber station, can, however, be comparatively different and can also be comparatively great. This is the reason why one must provide a time span as large as possible for the time delay. This technique, however, would mean an even longer additional holding of the connecting sets and the coupling network in practice of the known technique.